This invention relates to a method of improving the carding process in a card or a roller card unit wherein the carding cylinder is rotated by an electric drive motor and wherein the card operates in a working phase which is between an acceleration (start-up) phase and a deceleration (braking) phase.
In a known method the working rpm of the carding cylinder is fixed for determined types of fiber. Upon changing the fiber type, for example, from cotton to chemical fibers or conversely, the working rpm is changed by changing the mechanical transmission ratio between the drive motor and. the carding cylinder. This is effected, for example, by replacing the belt pulleys of appropriate diameter. Such an adjusting operation involves significant labor and delay, and only predetermined rpm changes are possible, dependent upon the structural design (stages) of the step-up or step-down arrangements. It is a further disadvantage of the known; arrangements that upon the inertia run of the cylinder, for example, upon braking following an interruption in operation, a larger quantity of fiber will accumulate on the cylinder than in the normal operational phase. This causes irregularities which, during the restart, may lead to a rupture in the fiber web or sliver. Even if such a rupture does not take place, a certain length of the web or sliver has to be removed to eliminate the above-noted irregularities. This makes unfeasible an automatic restart (re-threading) of the material, and thus losses of material will occur. The known arrangement utilizes a non-regulated drive motor, that is, during the processing of the fiber material, no rpm variation of the carding cylinder is intended because of the large inertia thereof. As a result, at the intended cylinder rpm too many fiber neps may remain in the fiber material.
It has been proposed to provide a switching unit in the current supply circuit for the drive motor of the licker-in/cylinder drive. By means of the switching unit a start-up or brake regulator circuit equipped with an a.c. setter may be operatively connected to the circuit of the motor for the licker-in/cylinder drive. The regulator may be disconnected after the start-up or braking step. With such an arrangement it is possible only to effect at the carding cylinder a constant acceleration or deceleration of the start-up or braking processes. There results a two-stage drive in which after the acceleration there is effected a switchover to the line current drive; that is, during the start-up or braking process a purposeful setting of predetermined rpm's is not intended and during the normal operating phase (line current supply) a variation of the cylinder rpm is not feasible at all.